The present invention relates generally to vehicle drive axle assemblies, and more particularly to a worm drive axle traction assembly.
Many types of mechanisms are used for providing traction control of a four-wheel drive vehicle. Presently, transfer cases utilizing various types of passive and active torque transfer couplings are utilized in order to provide traction control. In addition, various differential designs have been provided with passive and active traction control devices. A problem with current traction control devices is that they greatly contribute to the increased weight of the powertrain system.
Worm gearsets, otherwise referred to as worm/worm gear transmissions, are known in the mechanical power transmission field. The worm gear is driven by the rotation of the worm with which it meshes. The rotational speed of the associated shaft of the worm gear is a function of the number of teeth on the worm gear and the number of threads on the worm. The worm may be single or multiple threaded. Conventional worm/worm gear transmissions have a worm gear with at least 24 teeth. In particular, the American National Standard xe2x80x9cDesign of Industrial Double-Enveloping Wormgearsxe2x80x9d (ANSI/AGMA-6030-C87) recommends 24 as the minimum number of gear teeth. Moreover, standard double enveloping worm/worm gear transmissions have been used only for ratios of five and more. Due to such high ratios, it has been considered impractical to use the worm gear as the driven member and the worm as the driving member to transfer power from the worm gear to the worm.
Accordingly, it is an object of the present invention to provide a traction device for a four-wheel drive vehicle which is simple in construction.
It is another object of the present invention to provide a traction device for a four-wheel drive vehicle which is compact and reduced in weight.
These and other objects of the present invention are obtained by providing an axle traction assembly having a drive shaft with an enveloping worm mounted thereto. An enveloping worm gear is in meshing engagement with the is enveloping worm and is selectively engaged with left and right axle shafts by actuation of first and second clutches. The clutches are operatively controlled by a control system which detects relative rotation between the left and right axle shafts and provides appropriate signals to the first and second clutches in order to provide appropriate traction control. The use of a novel double enveloping worm/worm gear transmission allows the axle traction assembly to be reduced in weight and compact. In addition, a greater torque capacity is provided by the double enveloping worm and worm gear transmission which was previously only available with much larger gear systems.
The double enveloping worm/worm gear transmission of the present invention also provides quieter operation in comparison with prior gear devices.
Enveloping worm/worm gear transmissions with a worm gear having less than twenty-four teeth have not been commercially used because it was believed impossible to build such a transmission due to the need to undercut the root of the worm gear tooth. Thus, those skilled in the art did not consider enveloping type worm gears with less than twenty-four teeth to be feasible for commercial applications. In contrast, the enveloping worm/worm gear transmissions of the present invention utilize a worm gear without undercut gear teeth because of a greater enveloping angle for one revolution of the worm thread.
With less than twenty-four gear teeth and a greater enveloping angle for one revolution of the thread, as compared to prior enveloping worm/worm gear transmissions, the minimum ratio for one thread could be reduced to two. In contrast, prior enveloping worm/worm gear transmissions had a minimum ratio of twenty-four for one thread of the worm and a ratio of five for five threads of the worm. The efficiency of the new worm/worm gear transmission is even greater than that of well-known hypoid gearsets which are used in low ratio right angle drives. Thus, the present invention can replace hypoid or bevel gearing in many applications by reason of the low ratio. In addition, this new worm/worm gear transmission is able to back drive by transmitting torque from the worm gear to the worm. For the same size, this invention has more than twice the capacity of traditional hypoid gearing.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.